help with protein size

Hope someone has a suggestion here. I purchased an antibody from a company whose technical support said that the specificity of the antibody was confirmed by running a Western. Their band showed up around 105-105 kDa. I ran a Western with the antibody (both rat tissue which they used and my test tissue) and I am getting bands for both sets of tissue at about 50-52 kDa. I have tried using protease inhibitors, both an recipe and a inhibitor cocktail, and still have similar results. The antibody is a polyclonal, but I'm not sure how likely it is that it is now recognizing a different protein since it has already been tested in rat with a single band at 105. Also, FYI the protein is a dimer, but literature suggests that each subunit should be about 100-110 kDa, not the dimer. Any suggestions or explanations as to why this protein would be half the size of the normal?